Best DIY config for rotating frame on mast?

Discussion in 'Frame Construction' started by AdironDoc, Nov 4, 2010.

  1. AdironDoc

    AdironDoc WindyNation Engineer

    I have a 34ft mast with guy wires that's 1.25" at the top. My PMA and Windgrabbers will be fixed to a metal plate, tail/vane section. I'm wondering how the frame can be made to rotate freely at the top. I was thinking a caster with the wheel removed but I'm sure there are better ideas out there. Ideally a flat plate with bearings attached to a cylindrical end like the second drawing. Any thoughts?

  2. timber

    timber WindyNation Engineer

    Hi AdironDoc,

    Looks like no one has answered you so I'll give it a shot.
    I would venture a guess that a majority of yaw bearings consist of a piece of pipe (sleeve) placed over the top of the pole.
    A piece of steel plate welded perpendicular to that with some sort of bushing (brass or plastic washer) at the top of the pole works well.
    As long as the sleeve turns fairly easily over the pipe at the top of a tower or pole it should prove to be a good yaw bearing.
    When greased well, it should resist moisture and corrosion and keep the turning action smooth.

    Ball bearings or roller bearings will work as well but are not really necessary and can sometimes make the turning action too free.
    I think some resistance (friction) may actually help to keep the turbine from constantly seeking very slight variances in wind direction and concentrate more on the prevailing wind direction.

    Another consideration is that ball bearings consist of many moving parts and may be much more subject to dust and moisture entering and either clogging, wearing or corroding those many small surfaces.

    Now if you are like me, I don't weld so finding something off-the-shelf is desirable. A pipe flange could be bolted to a steel plate or frame and a piece of pipe could then be screwed into the flange to form the outer sleeve of the yaw bearing. As long as you place a washer or better yet two washers (steel, brass, bronze or dense plastic would work) at the top of the pole (inner sleeve) and the whole area is greased then you have a minimum number of moving parts, protected by grease. This will form a smooth action with slight resistance that will last for many, many years with little maintenance. Ball bearings would need to be cleaned and lubricated quite often to prevent corrosion and wear.
    If you use a bearing, I would be sure it sealed roller type bearing.

    Hope this helps,

  3. windyguru

    windyguru WindyNation Expert

    Timber's answer is dead on. The cheapest and easiest thing I could think of would be a pipe flange with a pipe threaded into it. Use extra strength Loctite if you are worried about it unthreading.

    For a cheap and very durable bushing you can get some UHMW polyethylene. Murray has some photos posted somewhere of his bushing.

    If you wind up using 1.5 inch Schedule 80 pipe for your tower, which is what the Windtura 500 complete kit is designed to mount on, you can get a machined bushing from us. Look on page 7 of the owner's manual to see how our bushing gets inserted into the tower pipe: ... Manual.pdf

    We do not really sell the bushings but if you want to buy one, send me an e-mail.

    One thing to keep in mind with a bushing. Make sure you sand smooth the metal parts of the turbine that are going to come in contact with the bushing. Once in a while, especially if the nearby metal has been cut, drilled or welded, the metal can have jagged metal present. This just might be very small features on the metal that are hard to see. If they are present, they will score and scrap the plastic bushing and wear it out pretty quick. We have seen it happen. If you sand the metal with an orbital sander for 30 seconds, this solves the problem.

    If the metal is smooth, a 0.25 inch thick UHMW bushing should last literally 50 years.
  4. murray2paddles

    murray2paddles WindyNation Engineer

    UHMW polyethylene , I use two of these for bushings. Doesn't matter if there are any imperfections on the metal bases and if there are it works even better. This allows the bushings to turn on each other with not metal against bushing wear. Probably do not need it but I grease them up also. We have come a long way in turbine mounts in a short time. I agree with Timber that a pipe over pipe is the easiest and least amount of maintenance. See bottom of page 1 on mount ideas for a Windy 500.

  5. windyguru

    windyguru WindyNation Expert

    Yes, if you have two pieces of UHMW then no sanding of the metal would be necessary.

    Our design uses one piece. We tested it on sanded metal and it had virtually zero wear. I would say the bushing will out live the owner in this scenario. On a piece of metal with laser splatter from being cut by a laser, I would give the bushing 6 months. The laser splatter acts like low grit sand paper.

    Obviously, we sand the bottom of our Windtura mounts where the bushing sits.
  6. AdironDoc

    AdironDoc WindyNation Engineer

    Thanks everyone and thanks for the replies! I had ordered two sets of pillow block bearings to fit over the 1.25" top section of my 34' telescoping mast but they have to be seen to be believed! The bore is spot on, but the bearings weigh like 5lbs each and look like they could support a ton. Anyway, I did cobble something together using a large elbow bracket bolted to galvanized L-bracket with a diagonal brace. Functional but ugly.

    Got inspired by someone's PVC design and will now use PVC and the advice you all gave regarding letting the pole slip into the larger pole. A 4" PVC front section, $" x 2" San-Tee with a reducer down to a 3/4" galvanized 2ft rod. The tail will be 2" with slot cut for a plexi-glass vane. I wish I could figure out how to make it furl with a PVC construction!

    I learned the hard way that 1" galvanized will NOT fit into the 1-1/4" bore of the mast. The outer diameter of the 1" galvanized is larger than 1-1/4". No problem. I'll pick up a length of 3/4" today and some plastic bushings as suggested. Greased up it should be fine, as you say.

    Any tips on length of tail/area of vane? My rotor is a 5 blade 24" windgrabber on a WindBlue lookalike. Thanks again for steering me in the right direction.

  7. AdironDoc

    AdironDoc WindyNation Engineer

    Ok, so after coming home with a cart full of PVC parts for the mount, tailpiece, and an assortment of 2 ft lengths of steel pipes, I notice immediately I have a problem. For the section that should slide down into the mast and rotate freely, I see that none of my steel pipe selections will fit inside the 1-1/4" thin walled galvanized mast. In fact, any pipe that would ends up with an internal diameter too small for proper wires. I concede that I will need to place a larger pipe over the top of the mast, sort of a "reverse" of what I was thinking. Now placing the steel bushings is not quite as simple, nor is figuring out what two surfaces will actually come together during rotation. A box of returns to Home Depot and another lesson learned. Placing the PMA slightly off center and figuring out how to hinge a 2" PVC to furl upwards diagonally? I haven't begun to think of it yet!

  8. murray2paddles

    murray2paddles WindyNation Engineer

    :lol: :lol: hang in there doc, you are on a roll.

    now that you are going outside on the mast all you have to do is look for a large steel washer at Home Depot or some hardware store that is the same size or larger than the OD of your mast pipe. As long as the mount pipe can clear it you are ok. It will already have the hole for your wires. Then you will have a flat metal surface to rotate on.

    if you want to use those washers as your bushings go for it , just make sure they are very smooth as Josh has said. Or you can place a few pieces of that plastic or nylon material between the steel bushings. If you do not have access to the material we suggested you can always just cut up a piece of crazy carpet as a gasket ( grease it up ) between the steel and away you go.,.

    good luck over the weekend.
  9. AdironDoc

    AdironDoc WindyNation Engineer

    Thanks for the pep talk, Murray! I ran a test of the WindyNation Windgrabbers on my PMA and had great results. I also scrapped the PVC mount idea. Although it looked better than iron, it's weaker at critical points and can't support a hinged tail. I cobbled together a PVC sleeve with threaded cap. Together with a steel bar, it should stay lightweight and plenty strong. Any formula or tips on how far off center to place the PMA to help furling? How far forward to put the PMA? should the yaw point be determined by balancing the frame?

    My attempt at the mast and coming up with a spring-hinged furling vane:
  10. timber

    timber WindyNation Engineer

    Hi AdironDoc,

    Great video, worth well over a thousand words.
    Looks like you are well on your way.

    How far off center is a bit of a balancing act (no pun intended) with length and action of the tail section and tail fin area.
    What I have found is that anywhere around 3-5 inch (Centerline to Centerline) should work fine.

    Looking from the front of the motor/ blade, you will want the motor offset to the right side of the yaw bearing.
    Your tail section will need to angle slightly (perhaps 10 degrees) to the left as viewed from the front of the motor to compensate for the motor offset.
    In other words, even though the blades tend to track mostly perpendicular to the wind direction the offset yaw will allow some rotation around it's axis. The tail angle will counter that rotation to keep the blades facing directly into the wind. (balancing act)

    The motor (turbine or actually alternator) only needs to be forward of the yaw, far enough to balance out the tail weight. (another balancing act)

    If using a spring, it won't take much tension at all, I'd start out with light duty spring(s) with hardly any tension, you can always tighten those if the turbine yaws at too low of a wind speed. (Ideally, it should probably yaw at somewhere around 25 mph winds, depending on what alternator you use.)

    Good luck, hope this helps,

  11. timber

    timber WindyNation Engineer


    Something like the above is an Ideal furling tail setup.
    Be sure that, when furled, the tail won't be able to hit the blades.
    You may need a stop of some sort to prevent this.

  12. timber

    timber WindyNation Engineer

    Opps, here's the picture ...


    Sorry about that, must have a bug in my computer ...



    Attached Files:

  13. AdironDoc

    AdironDoc WindyNation Engineer

    Hey thanks Timber!

    That's good info. So from what you've gone over, I should be planning 3 to 5 inches from center of yaw point to the rotor of the PMA. Additionally, the tail will be an inch or two to the opposite side to balance the weight? I remember reading sometime back that the length of the tail section should be approximately equal to the radius of the turbine. There was also a calculation on wind vane area. Can you tell me anything about that, or about how far in front of the yaw axis the PMA should be mounted? Most PMAs seem to be as close to the mast as possible.

    In the drawing, I notice that the furling mechanism folds and at maximum furling, hits a stopper. The diagram shows furling in one direction. The WindyNation video on assembling the kit seems to show the furling vane with a stop too. Shouldn't furling vanes furl in two directions? Maybe I'm missing something.

    Thanks for sharing your wisdom,

  14. timber

    timber WindyNation Engineer

    Hi AdironDoc,

    Only needs to furl in one direction. Actually it's the turbine that furls around the yaw bearing while the tail remains downwind.

    When you get a very high speed wind, the wind will push against the blades and tend to push the turbine (blades and all except tail) around the axis of the yaw bearing. The turbine will rotate around on the same side of the yaw bearing that the turbine is mounted.

    During normal wind conditions (slower than furling wind speed) the tail which is angled 10 deg (or so) to the left side (as viewed from front) will keep the turbine from rotating around the yaw bearing (or keep the blades facing the wind).
    During high wind conditions the tail will remain right where it is (down wind) as the turbine rotates around the yaw bearing (as described above.)


    Imagine not having a tail.
    The turbine is offset several inches from the yaw bearing. (right side as viewed from front)
    When the wind blows, it would tend to rotate the turbine around the yaw bearing until the blades were out of the wind.

    Now add the tail with fin, angled 10 deg to the opposite side of the yaw bearing as the turbine. (as in the picture in last post)
    Now the turbine won't tend to rotate around the yaw bearing because there is an equal force of wind on both the tail (with fin) to the left and the turbine (with blades) to the right. (That is, of course, until you get very high wind speed ... then the turbine will rotate but the tail will stay true to the wind.)
    The stop will prevent the turbine from rotating too far where it would hit the stationary tail.

    Correct, tail length should be equal to around half the diameter of the wind swept area. (From what I've read.)

    Turbine distance in front of the yaw bearing ... I'm not really sure how critical this is, other than the fact that you want as little stress on things as possible so having everything fairly evenly balanced is probably best. I tend to place my turbine just forward of the yaw bearing due to ease of mounting hardware for the yaw bearing. I would imagine that the center of gravity of the assembled turbine, frame, bearing and tail is about right.

    My research on tail fin area leads me to believe that the tail fin area should be approximately 1/16 the wind swept area.
    Like everything else it depends on a number of variables and the best size is whatever works best and may take some trial and error.
    I got my information about this from or their forum
    I've been reading that forum for a number of years and trust several people there who have made many, many wind turbines.

    Please take any of the information that I provide with a grain of salt, I share what has worked for me but that doesn't mean that it's the only way or even the correct way ... it's just the way I would make it or what I believe to be true from my research.
    I always hope others who disagree or know better will feel free to correct me if I'm wrong. Working together we all have something to gain.

  15. timber

    timber WindyNation Engineer


    FYI: The sketch above of the yaw angle was from the Otherpower site. The offset from the yaw centerline is a lot in the sketch, I would not recommend having such a huge offset with these smaller turbines (right next to the bearing, as you noted seems more appropriate). I believe the sketch is for a 10 or 15 foot diameter axial flux type alternator so the application is quite different with that large a windswept area, however, the general principal of the furling mechanism is the same.

  16. AdironDoc

    AdironDoc WindyNation Engineer

    Awesome post, Timber! Now I got it! I thought I understood the two opposing forces around the yaw point, but now I see the tail doesn't fold as so often appears in videos, its the PMA folding on the tail. That the furling is in one direction also simplifies things for me as now I can remove one of the two springs from my tail design so the hinge simply bumps up against a "neutral" point.

    Thanks for taking the time to help me. I'll be recording a short video when I have the pieces laid out for a "new and improved design". ;)

  17. windyguru

    windyguru WindyNation Expert

  18. timber

    timber WindyNation Engineer

    That's an excellent video of furling in action Windy!
    Great resource.

  19. AdironDoc

    AdironDoc WindyNation Engineer

    Agree with Timber, Windy. Good video where I see that the tail didn't move away, it was the rotor. Very illustrative and also a good view of the relative positions of the PMA vs Yaw and vane. I may scrap the spring hinge design of the tail and go with a gravity activated system. With the 1" galvanized perforated channel I'm using, adding a 20 degree bar is a snap. I plan on using a threaded 1/4" stainless rod, push it through one of the perforations vertically, bolt it down, and put an immediate 20 degree bend on it. I have galvanized EMT to use as a sleeve over the threaded rod, or maybe even go with PVC through which I'll drill at a 20 degree angle and add some bushings. Finally coming together in my head. Thanks guys!

    Adding what I learned from Timber, I've added part 2 to my blog/chronicle. Cheers!

  20. timber

    timber WindyNation Engineer

    Don't forget to make a "stop" so the blades stay clear of the tail when furled.
    I have a stop in the opposite direction as well to keep the tail in line, so the full range of tail swing is about 90 degrees total.
    I'll check out your video too.


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